p53 loss and point mutations are associated with suppression of apoptosis and progression of CML into myeloid blastic crisis

CX‑5461 potentiates imatinib‑induced apoptosis in K562 cells by stimulating KIF1B expression

The selective RNA polymerase I inhibitor CX-5461 has been shown to be effective in treating some types of leukemic disorders. Emerging evidence suggests that combined treatments with CX-5461 and other chemotherapeutic agents may achieve enhanced effectiveness as compared with monotherapies. Currently, pharmacodynamic properties of the combination of CX-5461 with tyrosine kinase inhibitors remain to be explored. The present study tested whether CX-5461 could potentiate the effect of imatinib in the human chronic myeloid leukemia cell line K562, which is p53-deficient. It was demonstrated that CX-5461 at 100 nM, which was non-cytotoxic in K562 cells, potentiated the pro-apoptotic effect of imatinib. Mechanistically, the present study identified that the upregulated expression of kinesin family member 1B (KIF1B) gene might be involved in mediating the pro-apoptotic effect of imatinib/CX-5461 combination. Under the present experimental settings, however, neither CX-5461 nor imatinib alone exhibited a significant effect on KIF1B expression. Moreover, using other leukemic cell lines, it was demonstrated that regulation of KIF1B expression by imatinib/CX-5461 was not a ubiquitous phenomenon in leukemic cells and should be studied in a cell type-specific manner. In conclusion, the results suggested that the synergistic interaction between CX-5461 and imatinib may be of potential clinical value for the treatment of tyrosine kinase inhibitor-resistant chronic myeloid leukemia.

Treatment of blast phase chronic myeloid leukaemia: A rare and challenging entity

Despite the success of BCR-ABL-specific tyrosine kinase inhibitors (TKIs) such as imatinib in chronic phase (CP) chronic myeloid leukaemia (CML), patients with blast phase (BP)-CML continue to have a dismal outcome with median survival of less than one year from diagnosis. Thus BP-CML remains a critical unmet clinical need in the management of CML. Our understanding of the biology of BP-CML continues to grow; genomic instability leads to acquisition of mutations which drive leukaemic progenitor cells to develop self-renewal properties, resulting in differentiation block and a poor-prognosis acute leukaemia which may be myeloid, lymphoid or bi-phenotypic. Similar advances in therapy are urgently needed to improve patient outcomes; however, this is challenging given the rarity and heterogeneity of BP-CML, leading to difficulty in designing and recruiting to prospective clinical trials. This review will explore the treatment of BP-CML, evaluating the data for TKI therapy alone, combinations with intensive chemotherapy, the role of allogeneic haemopoietic stem cell transplantation, the use of novel agents and clinical trials, as well as discussing the most appropriate methods for diagnosing BP and assessing response to therapy, and factors predicting outcome.

The Downregulation of Both Giant HERCs, HERC1 and HERC2, Is an Unambiguous Feature of Chronic Myeloid Leukemia, and HERC1 Levels Are Associated with Leukemic Cell Differentiation

Large HERC E3 ubiquitin ligase family members, HERC1 and HERC2, are staggeringly complex proteins that can intervene in a wide range of biological processes, such as cell proliferation, DNA repair, neurodevelopment, and inflammation. Therefore, mutations or dysregulation of large HERCs is associated with neurological disorders, DNA repair defects, and cancer. Though their role in solid tumors started to be investigated some years ago, our knowledge about HERCs in non-solid neoplasm is greatly lagging behind. Chronic Myeloid Leukemia (CML) is a model onco-hematological disorder because of its unique and unambiguous relation between genotype and phenotype due to a single genetic alteration. In the present study, we ascertained that the presence of the BCR-ABL fusion gene was inversely associated with the expression of the HERC1 and HERC2 genes. Upon the achievement of remission, both HERC1 and HERC2 mRNAs raised again to levels comparable to those of the healthy donors. Additionally, our survey unveiled that their gene expression is sensitive to different Tyrosine Kinases Inhibitors (TKIs) in a time-dependent fashion. Interestingly, for the first time, we also observed a differential HERC1 expression when the leukemic cell lines were induced to differentiate towards different lineages revealing that HERC1 protein expression is associated with the differentiation process in a lineage-specific manner. Taken together, our findings suggest that HERC1 might act as a novel potential player in blood cell differentiation. Overall, we believe that our results are beneficial to initiate exploring the role/s of large HERCs in non-solid neoplasms.

Understanding and Monitoring Chronic Myeloid Leukemia Blast Crisis: How to Better Manage Patients

Chronic myeloid leukemia (CML) is triggered primarily by the t(9;22) (q34.13; q11.23) translocation. This reciprocal chromosomal translocation leads to the formation of the BCR-ABL fusion gene. Patients in the chronic phase (CP) experience a good curative effect with tyrosine kinase inhibitors. However, cases are treatment refractory, with a dismal prognosis, when the disease has progressed to the accelerated phase (AP) or blast phase (BP). Until now, few reports have provided a comprehensive description of the mechanisms involved at different molecular levels. Indeed, the underlying pathogenesis of CML evolution comprises genetic aberrations, chromosomal translocations (except for the Philadelphia chromosome), telomere biology, and epigenetic anomalies. Herein, we provide knowledge of the biology responsible for blast transformation of CML at several levels, such as genetics, telomere biology, and epigenetic anomalies. Because of the limited treatment options available and poor outcomes, only the therapeutic response is monitored regularly, which involves BCR-ABL transcript level assessment and immunologic surveillance, with the optimal treatment strategy for patients in CP adapted to evaluate disease recurrence or progression. Overall, selecting optimal treatment endpoints to predict survival and successful TFR improves the quality of life of patients. Thus, identifying risk factors and developing risk-adapted therapeutic options may contribute to a better outcome for advanced-phase patients.

Novel Benzenesulfonate Scaffolds with a High Anticancer Activity and G2/M Cell Cycle Arrest

Sulfonates, unlike their derivatives, sulphonamides, have rarely been investigated for their anticancer activity. Unlike the well-known sulphonamides, esters are mainly used as convenient intermediates in a synthesis. Here, we present the first in-depth investigation of quinazoline sulfonates. A small series of derivatives were synthesized and tested for their anticancer activity. Based on their structural similarity, these compounds resemble tyrosine kinase inhibitors and the p53 reactivator CP-31398. Their biological activity profile, however, was more related to sulphonamides because there was a strong cell cycle arrest in the G2/M phase. Further investigation revealed a multitargeted mechanism of the action that corresponded to the p53 protein status in the cell. Although the compounds expressed a high submicromolar activity against leukemia and colon cancers, pancreatic cancer and glioblastoma were also susceptible. Apoptosis and autophagy were confirmed as the cell death modes that corresponded with the inhibition of metabolic activity and the activation of the p53-dependent and p53-independent pathways. Namely, there was a strong activation of the p62 protein and GADD44. Other proteins such as cdc2 were also expressed at a higher level. Moreover, the classical caspase-dependent pathway in leukemia was observed at a lower concentration, which again confirmed a multitargeted mechanism. It can therefore be concluded that the sulfonates of quinazolines can be regarded as promising scaffolds for developing anticancer agents.

Examination of clinically-derived p210 BCR/ABL1 RhoGEF mutations in a murine bone marrow transplantation model of CML

Expression of the p210 BCR/ABL1 fusion protein has been described in virtually all patients with chronic myelogenous leukemia (CML). Previous studies have identified a guanine nucleotide exchange factor (RhoGEF) domain within BCR that is retained in p210 BCR/ABL1. Missense mutations at residues T654 (T654K) and F547 (F547L) within this domain have been reported in a CML patient in blast crisis (BC). In this study, we have evaluated p210 BCR/ABL1 constructs that contain these substitutions in a murine bone marrow transplantation (BMT) model of CML. The mutants exhibit normal expression and tyrosine kinase activity but altered signaling. When examined in the BMT assay, mice that express the mutants exhibit earlier onset of disease but have significantly extended lifespans relative to mice that express unmodified p210 BCR/ABL1. While mice that express p210 BCR/ABL1 exhibit neutrophilia that progresses to a less differentiated phenotype at death, disease in the mutant mice is characterized by eosinophilia with no maturation arrest. This observation was confirmed in vitro using myeloid cells and was associated with enhanced p53 phosphorylation and G1/S arrest. These results suggest that residues within the RhoGEF domain of p210 BCR/ABL1 can influence disease progression.

Chronic Myeloid Leukemia Following Treatment for Primary Neoplasms or Other Medical Conditions

OBJECTIVES

Therapy-related chronic myeloid leukemia (CML) has been reported, but its clinical presentation and pathologic features have not yet been well characterized.

METHODS

Twenty-one cases of CML following treatment for primary diseases were collected and retrospectively analyzed.

RESULTS

The clinical presentation, pathologic features, and cytogenetic profile were similar to de novo CML. In particular, those with an isolated Philadelphia chromosome constituted 88.9% of our cases, and additional aberrations characteristic of therapy-related acute myeloid leukemia/myelodysplastic syndrome (AML/MDS) were not identified in this study. The patients responded to imatinib/derivatives and survived with limited follow-up.

CONCLUSIONS

Therapy-related CML has a clinical presentation, pathologic features, and cytogenetic profile akin to de novo CML. Absence of additional significant aberrations seems to suggest a pathogenesis different from therapy-related AML/MDS. Therapy-related CML exhibits a robust therapeutic response to imatinib/derivatives and favorable clinical outcomes similar to de novo CML.

p53 modulates the effect of ribosomal protein S6 kinase1 (S6K1) on cisplatin toxicity in chronic myeloid leukemia cells

Chronic myeloid leukemia (CML) is characterized by the expression of the oncoprotein, BCR-ABL. BCR-ABL inhibitors revolutionized CML chemotherapy while blast crisis (BC) CML patients are less responsive. Since suppression of ribosomal protein S6 kinase1 (S6K1) phosphorylation reverses the resistance to BCR-ABL inhibitor in CML cells and S6K1 inhibitors augment cisplatin toxicity in lung cancer cells, we speculated that combination of S6K1 inhibitor and cisplatin may be beneficial for eliminating BC CML cells. To our surprise, S6K1 inhibition decreased cisplatin-induced DNA damage and cell death only in p53^-/- BC CML cells but not in p53^+/+ BC CML cells. During the progression of CML, p53 expression either decreases or mutates. Moreover, the expression of p53 affects drug response of CML cells. Our results confirmed that S6K1 inhibition reversed cisplatin toxicity is dependent on p53 expression in CML cells. Moreover, p53 attenuated the phosphorylation and localization of S6K1 via attenuating 3-phosphoinositide dependent protein kinase-1 (PDK1) phosphorylation. Furthermore, S6K1 acts via DNA-PKcs to regulate H2AX phosphorylation and PARP cleavage, respectively. Taken together, our results suggest that p53/PDK1/S6K1 is a novel pathway regulating cisplatin toxicity in BC CML cells.

Natural course and biology of CML

Chronic myeloid leukaemia (CML) is a myeloproliferative disorder arising in the haemopoietic stem cell (HSC) compartment. This disease is characterised by a reciprocal t(9;22) chromosomal translocation, resulting in the formation of the Philadelphia (Ph) chromosome containing the BCR-ABL1 gene. As such, diagnosis and monitoring of disease involves detection of BCR-ABL1. It is the BCR-ABL1 protein, in particular its constitutively active tyrosine kinase activity, that forges the pathogenesis of CML. This aberrant kinase signalling activates downstream targets that reprogram the cell to cause uncontrolled proliferation and results in myeloid hyperplasia and 'indolent' symptoms of chronic phase (CP) CML. Without successful intervention, the disease will progress into blast crisis (BC), resembling an acute leukaemia. This advanced disease stage takes on an aggressive phenotype and is almost always fatal. The cell biology of CML is also centred on BCR-ABL1. The presence of BCR-ABL1 can explain virtually all the cellular features of the leukaemia (enhanced cell growth, inhibition of apoptosis, altered cell adhesion, growth factor independence, impaired genomic surveillance and differentiation). This article provides an overview of the clinical and cell biology of CML, and highlights key findings and unanswered questions essential for understanding this disease.

Genomic instability in chronic myeloid leukemia: targets for therapy?

Philadelphia positive (Ph+) chronic myeloid leukemia (CML) is characterized by the occurrence of nonrandom genetic and cytogenetic abnormalities during disease progression. Many of these abnormalities are markers for genes which, when altered, can drive the blastic transformation process. Thus, such genetic alterations may be manifestations of an underlying genomic instability resulting from a compromised DNA damage and repair response, leading to advanced stages of CML and resistance to therapy. This article examines the molecular pathways that may lead to genomic instability in CML and the potential of these pathway constituents to be therapeutic targets.

“Acute myelogenous leukemia like” translocations in CML blast crisis: Two new cases of inv(16)/t(16;16) and a review of the literature

We describe two patients with CML blast crisis with clonal evolution affecting 16q22 (t(16;16)(p13;q22) and inv(16)(p13;q22), abnormalities of core binding factor, usually found in de novo acute myeloid leukemia (AML)). The bone marrow of both cases showed myelomonocytic (M4) differentiation and eosinophilia. Both patients had prominent extramedullary disease and had poor response to treatment. A literature search focused on patients with CML and additional chromosome changes more typical of AML, revealed that the morphology of the blasts correlated with the finding typical of the underlying "AML" cytogenetic abnormality and an overall very poor clinical outcome, even in the groups with "favorable" AML type translocations.

The absence of p53 is critical for the induction of apoptosis by 5-aza-2'-deoxycytidine

The absence of functional p53 has complex consequences on the cellular responses to cytotoxic drugs. Here, we have examined the role of p53 in the response to 5-aza-2'-deoxycytidine (5-aza-dC or decitabine). Primary mouse embryonic fibroblasts deficient for p53 undergo apoptosis after treatment with 5-aza-dC. When compared with other demethylating drugs or chemotherapeutic treatments, 5-aza-dC showed the highest selectivity ratio for triggering apoptosis in p53-deficient cells relative to wild-type cells. Moreover, the apoptotic efficacy of 5-aza-dC is proprietary of p53-deficient cells, not being observed in cells lacking other cell-cycle regulators, such as p19ARF, p16INK4a, p21(CIP1/WAF1), E2F-1, or E2F-2. Interestingly, treatment with 5-aza-dC results in the same degree of global genomic hypomethylation in wild-type and p53-null cells. However, wild-type cells activate p53 and arrest at G2/M, whereas p53-null cells accumulate severe chromosomal aberrations and undergo apoptosis. Significantly, the impact of p53-deficiency on the response to 5-aza-dC is not exclusive of primary non-neoplastic cells, but it is also present in neoplastically transformed cells. Finally, treatment of mice bearing genetically defined tumors with nontoxic doses of 5-aza-dC results in therapeutical responses only on tumors lacking p53, but not on tumors lacking p19ARF. Together, our results put forward the hypothesis that the absence of p53 may determine a higher chemotherapeutic index for 5-aza-dC.

Chronic myeloid leukemia: pathophysiology, diagnostic parameters, and current treatment concepts

Chronic myeloid leukemia (CML) is a stem cell disease characterized by excessive accumulation of clonal myeloid (precursor) cells in hematopoietic tissues. CML cells display the translocation t(9; 22) that creates the bcr/abl oncogene. The respective oncoprotein (= BCR/ABL) exhibits constitutive tyrosine kinase activity and promotes growth and survival in CML cells. Clinically, CML can be divided into three phases: the chronic phase (CP), the accelerated phase (AP), and the blast phase (BP) that resembles acute leukemia. Progression to AP and BP is associated with occurrence of additional genetic defects that cooperate with bcr/abl in leukemogenesis and lead to resistance against antileukemic drugs. The prognosis in CML is variable depending on the phase of disease, age, and response to therapy. The only curative approach available to date is stem cell transplantation. For those who cannot be transplanted, the BCR/ABL tyrosine kinase inhibitor STI571 (Glivec, Imatinib), interferon-alpha (with or without ARAC), or other cytoreductive drugs are prescribed. Currently available data show that STI571 is a superior compound compared to other drugs in producing complete cytogenetic and molecular responses. However, despite superior initial data and high expectations for an effect on survival, long term results are not available so far, and resistance against STI571 has been reported. Forthcoming strategies are therefore attempting to prevent or counteract STI571 resistance by co-administration of other antileukemic drugs. Whether these strategies will lead to curative drug therapy in CML in the future remains at present unknown.

Chronic myelogenous leukemia as a paradigm of early cancer and possible curative strategies

The chronological history of the important discoveries leading to our present understanding of the essential clinical, biological, biochemical, and molecular features of chronic myelogenous leukemia (CML) are first reviewed, focusing in particular on abnormalities that are responsible for the massive myeloid expansion. CML is an excellent target for the development of selective treatment because of its highly consistent genetic abnormality and qualitatively different fusion gene product, p210(bcr-abl). It is likely that the multiple signaling pathways dysregulated by p210(bcr-abl) are sufficient to explain all the initial manifestations of the chronic phase of the disease, although understanding of the circuitry is still very incomplete. Evidence is presented that the signaling pathways that are constitutively activated in CML stem cells and primitive progenitors cooperate with cytokines to increase the proportion of stem cells that are activated and thereby increase recruitment into the committed progenitor cell pool, and that this increased activation is probably the primary cause of the massive myeloid expansion in CML. The cooperative interactions between Bcr-Abl and cytokine-activated pathways interfere with the synergistic interactions between multiple cytokines that are normally required for the activation of stem cells, while at the same time causing numerous subtle biochemical and functional abnormalities in the later progenitors and precursor cells. The committed CML progenitors have discordant maturation and reduced proliferative capacity compared to normal committed progenitors, and like them, are destined to die after a limited number of divisions. Thus, the primary goal of any curative strategy must be to eliminate all Philadelphia positive (Ph+) primitive cells that are capable of symmetric division and thereby able to expand the Ph+ stem cell pool and recreate the disease. Several highly potent and moderately selective inhibitors of Bcr-Abl kinase have recently been discovered that are capable of killing the majority of actively proliferating early CML progenitors with minimal effects on normal progenitors. However, like their normal counterparts, most of the CML primitive stem cells are quiescent at any given time and are relatively invulnerable to the Bcr-Abl kinase inhibitors as well as other drugs. We propose that survival of dormant Ph+ stem cells may be the most important reason for the inability to cure the disease during initial treatment, while resistance to the inhibitors and other drugs becomes increasingly important later. An outline of a possible curative strategy is presented that attempts to take advantage of the subtle differences in the proliferative behavior of normal and Ph+ stem cells and the newly discovered selective inhibitors of Bcr-Abl. Leukemia (2003) 17, 1211-1262. doi:10.1038/sj.leu.2402912

BCR/ABL regulates response to DNA damage: the role in resistance to genotoxic treatment and in genomic instability

BCR/ABL regulates cell proliferation, apoptosis, differentiation and adhesion. In addition, BCR/ABL can induce resistance to cytostatic drugs and irradiation by modulation of DNA repair mechanisms, cell cycle checkpoints and Bcl-2 protein family members. Upon DNA damage BCR/ABL not only enhances reparation of DNA lesions (e.g. homologous recombination repair), but also prolongs activation of cell cycle checkpoints (e.g. G2/M) providing more time for repair of otherwise lethal lesions. Moreover, by modification of anti-apoptotic members of the Bcl-2 family (e.g. upregulation of Bcl-x(L)) BCR/ABL provides a cytoplasmic 'umbrella' protecting mitochondria from the 'rain' of apoptotic signals coming from the damaged DNA in the nucleus, thus preventing release of cytochrome c and activation of caspases. The unrepaired and/or aberrantly repaired (but not lethal) DNA lesions resulting from spontaneous and/or drug-induced damage can accumulate in BCR/ABL-transformed cells leading to genomic instability and malignant progression of the disease. Inhibition of BCR/ABL kinase activity by STI571 (Gleevec, imatinib mesylate) reverses drug resistance and, in combination with standard chemotherapeutics can exert strong anti-leukemia effect.

Breakpoint characterization of der(9) deletions in chronic myeloid leukemia patients

Deletions adjacent to the 9/22 translocation breakpoint on the derivative chromosome 9 have recently been described in a substantial number of chronic myeloid leukemia (CML) cases, but their extension has not been characterized in detail. Using FISH with an appropriate set of BAC/PAC probes, we have characterized the deletion in 10 CML cases, identified by screening 71 patients at diagnosis. Five patients showed a complex chromosome rearrangement and 3 of them were deleted. The size of the deletion was variable, ranging from few hundreds kb to 8 Mb. A minimally deleted region on both chromosomes 9 and 22 was identified and was found to contain the ASS gene on chromosome 9 and IGLL1 on chromosome 22.

Chronic myelogenous leukemia: mechanisms underlying disease progression

Chronic myelogenous leukemia (CML), characterized by the BCR-ABL gene rearrangement, has been extensively studied. Significant progress has been made in the area of BCR-ABL-mediated intracellular signaling, which has led to a better understanding of BCR-ABL-mediated clinical features in chronic phase CML. Disease progression and blast crisis CML is associated with characteristic non-random cytogenetic and molecular events. These can be viewed as increased oncogenic activity or loss of tumor suppressor activity. However, what causes transformation and disease progression to blast crisis is only poorly understood. This is in part due to the lack of a good in vivo model of chronic phase CML even though animal models developed over the last few years have started to provide insights into blast crisis development. Thus, additional in vitro and in vivo studies will be needed to provide a complete understanding of the contribution of BCR-ABL and other genes to disease progression and to improve therapeutic approaches for blast crisis CML.

Evaluation of relationship between chromosome 22 and p53 gene alterations and the subtype of meningiomas by the interphase-FISH technique

In this study, we investigated the relationship between genetic alterations such as chromosome 22 aneuploidy and p53 gene deletion, and the pathological types of meningioma of typical and aggressive forms. Thirty-four meningiomas (23 typical and 11 aggressive) were examined by application of fluorescence in situ hybridization (FISH) with chromosome 22 specific alpha satellite probe and a combination of p53 locus specific and chromosome 17 centromere specific alpha satellite probes, to evaluate the chromosome 22 aneuploidy and gain or loss of p53 gene along with chromosome 17. The results showed that, although chromosome 22 aneuploidy was seen in 7 out of 23 typical (30.4%) and 4 out of 11 aggressive meningiomas (36.3%), no p53 deletion was detected in typical meningiomas, and p53 deletion was detected in 3 out of 11 aggressive meningiomas (1 atypical and 2 malignant), which had recurrence. There were no simultaneous occurrences of p53 gene deletions between typical and aggressive meningiomas. The present findings indicate that the loss of chromosome 22 may be involved with tumorogenesis of typical and aggressive meningiomas, while p53 gene deletions may be involved with malignant progression and recurrence in the aggressive meningiomas.

From genes to therapy: the case of Philadelphia chromosome-positive leukemias

The Philadelphia chromosome (Ph-chromosome) has long represented the only cytogenetic abnormality known to be associated with a specific malignant disease in humans, being present in more than 95% of patients with chronic myelogenous leukemia. This abnormality is the result of a reciprocal translocation between the long arms of chromosome 9 and 22, t(9;22)(q34;q11), and its presence is not restricted to chronic myelogenous leukemia, but can also be found in 30% of cases of acute lymphoblastic leukemia in adults. In the 1980s, the molecular counterpart of the chromosomal rearrangement was identified to consist of the juxtaposition of parts of the BCR and ABL genes to form a BCR-ABL hybrid gene. The resulting chimeric proteins (P210 and P190), which retain constitutively activated tyrosine kinase activity, have demonstrated a causative role in the genesis of the leukemic process. Although many aspects of the BCR-ABL driven transformation remain unsolved, great advances in understanding the molecular pathology of Ph-positive leukemias resulted in meaningful improvement in the clinical setting. Molecular tools to diagnose disease (PCR, FISH, and southern blot) and to monitor minimal residual disease after potential curative treatment are now in current practice, and new powerful therapeutic tools have emerged that target the molecular oncogenic pathways activated in Ph-positive cells. Among them, specific ABL tyrosine kinase inhibitors recently obtained extraordinary results in many clinical protocols. This review summarizes the most recent advances in this field with special focus on the putative mechanisms of the transformation and progression of chronic myelogenous leukemia and on the major impact that understanding the molecular biology of these diseases is having in clinical practice.

p53 expression in K562 cells is associated with caspase-mediated cleavage of c-ABL and BCR-ABL protein kinases

The chimaeric BCR-ABL oncoprotein is the molecular hallmark of chronic myeloid leukaemia (CML). Expression of Bcr-Abl has been associated with arrested differentiation as well as resistance to apoptosis. The downstream pathway involved in apoptosis resistance has been extensively studied, whereas the role of Bcr-Abl in cell differentiation is largely unclear. A recent report has shown that Bcr-Abl expression alone is sufficient to increase the number of multipotent and myeloid lineage-committed progenitors in a dose-dependent manner while suppressing the development of committed erythroid progenitors. In accordance with this model, downregulation of c-Abl and Bcr-Abl has been observed during differentiation in different systems, although the mechanism is still largely unknown. To investigate the relationship between erythroid differentiation and c-Abl and Bcr-Abl levels, we induced differentiation in K562 cells using a temperature-inducible p53 mutant (p53Val1335). It was found that p53-induced erythroid differentiation in K562 cells required caspase activity. During this process, caspase-dependent cleavage of c-Abl and Bcr-Abl tyrosine kinases was observed, suggesting a new mechanism for the downregulation of the kinases during erythroid differentiation.

p53-mediated downregulation of Chk1 abrogates the DNA damage-induced G2M checkpoint in K562 cells, resulting in increased apoptosis

BCR-ABL confers apoptotic resistance to a range of genotoxic agents, and this protection is mediated in part by prolonging the G2 checkpoint. The p53 tumour suppressor protein regulates the transcription of regulatory genes involved in cell cycle arrest and apoptosis. To investigate the effect of p53 on the BCR-ABL-mediated G2M checkpoint response, we transiently transfected the BCR-ABL-positive, p53-negative cell line K562 with wild-type human p53. The p53-transfected cells showed a decreased ability to arrest in G2 and an increase in apoptosis in response to etoposide treatment, relative to the control mock-transfected cells. p53-transfected and control cells were treated with etoposide and trapped at mitosis with nocodazole. The mitotic index of p53-transfected cells was higher than that of the control cells, which suggests that p53 abrogates the G2 checkpoint response to etoposide treatment in K562 cells. We found that the expression of the cell cycle checkpoint protein Chk1 was reduced in the etoposide-treated p53-transfected cells by 24 h, and this correlated with a reduction in the extent of etoposide-induced phosphorylation of CDK1 at tyrosine 15 (Y15). We conclude, therefore, that p53 overrides the strong G2 checkpoint response to etoposide in K562 cells, by directly or indirectly downregulating Chk1 expression, which, in turn, contributes to the proapoptotic effect of p53.

Molecular evolution of chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) is a clonal disorder of the pluripotent haematopoietic stem cell. The typical triphasic course of CML starts with the premalignant chronic phase initiated by BCR-ABL hybrid oncogene formation. Secondary genetic and epigenetic aberrations accompany the progression to the accelerated phase and fatal blastic crisis. Properly timed bone marrow transplantation in eligible patients can result in durable remissions or cure. Both of these states are often accompanied by a long-term persistence of quiescent leukaemic cells. Accordingly, a "functional cure" (i.e. tumour dormancy induction), rather than complete eradication of the malignant cells, is an adequate therapeutical goal. The level of the residual BCR-ABL-positive clones should be monitored and salvage treatment initiated whenever these quiescent leukaemic cells exit their dormant state.

Novel therapies for chronic myelogenous leukemia

The BCR-ABL oncogene is essential to the pathogenesis of chronic myelogenous leukemia, and immune mechanisms play an important role in control of this disease. Understanding of the molecular pathogenesis of chronic myelogenous leukemia has led to the development of several novel therapies, which can be broadly divided into therapies based on 1) inhibition of the BCR-ABL oncogene expression, 2) inhibition of other genes important to the pathogenesis of chronic myelogenous leukemia, 3) inhibition of BCR-ABL protein function, and 4) immunomodulation. We have systematically reviewed each of these novel therapeutic approaches in this article.

Loss of heterozygosity and heterogeneity of its appearance and persisting in the course of acute myeloid leukemia and myelodysplastic syndromes

Screening for loss of heterozygosity (LOH) of the panel of 18 highly polymorphic microsatellite markers, especially from the region 11p15, was carried out on 154 samples from 26 patients with acute myeloid leukemia and eight with myelodysplastic syndromes (MDS). LOH was detected at the majority (72%) of the loci tested: 47% of informative patients displayed LOH for at least one of the microsatellite locus from the region 11p15 and 23.5% of patients displayed LOH among the other markers tested within the study. A longitudinal follow-up of patients showed a remarkable heterogeneity of LOH appearance and its persistance during the course of the disease suggesting an intratumor clonal heterogeneity, or alternatively, presence of LOH in more than one cell clone. The data revealed two regions of high loss of one allele in 11p15.5, defined by markers D11S1363 and D11S1338, indicating that LOH at the subtelomeric region of the short arm of chromosome 11 is a much common event in hematological malignancies than it was previously reported.

Acquired, nonrandom chromosomal abnormalities associated with the development of acute promyelocytic leukemia in transgenic mice

We previously generated a transgenic mouse model for acute promyelocytic leukemia (APL) by expressing the promyelocytic leukemia (PML)-retinoic acid receptor (RARalpha) cDNA in early myeloid cells. This fusion protein causes a myeloproliferative disease in 100% of animals, but only 15-20% of the animals develop acute leukemia after a long latency period (6-13 months). PML-RARalpha is therefore necessary, but not sufficient, for APL development. The coexpression of a reciprocal form of the fusion, RARalpha-PML, increased the likelihood of APL development (55-60%), but did not shorten latency. Together, these results suggested that additional genetic events are required for the development of APL. We therefore evaluated the splenic tumor cells from 18 transgenic mice with APL for evidence of secondary genetic events, by using spectral karyotyping analysis. Interstitial or terminal deletions of the distal region of one copy of chromosome 2 [del(2)] were found in 1/5 tumors expressing PML-RARalpha, but in 11/13 tumors expressing both PML-RARalpha and RARalpha-PML (P < 0.05). Leukemic cells that contained a deletion on chromosome 2 often contained additional chromosomal gains (especially of 15), chromosomal losses (especially of 11 or X/Y), or were tetraploid (P </= 0.001). These changes did not commonly occur in nontransgenic littermates, nor in aged transgenic mice that did not develop APL. These results suggest that expression of RARalpha-PML increases the likelihood of chromosome 2 deletions in APL cells. Deletion 2 appears to predispose APL cells to further chromosomal instability, which may lead to the acquisition of additional changes that provide an advantage to the transformed cells.

c-Myc antagonizes the effect of p53 on apoptosis and p21WAF1 transactivation in K562 leukemia cells

c-myc protooncogene positively regulates cell proliferation and overexpression of c-myc is found in many solid tumors and leukemias. In the present study we used the K562 human myeloid leukemia cell line as a model to study the functional interaction between c-Myc and p53. Using two different methods, we generated K562 transfectant cell lines with conditional expression of either c-Myc or p53. The cells expressed the p53Vall35 mutant, which adopts a wild-type conformation at 32 degrees C, while c-Myc induction was achieved with a zinc-inducible expression vector. We found that p53 in wild-type conformation induces growth arrest and apoptosis of K562. Expression of c-Myc significantly attenuated apoptosis and impaired the transcriptional activity of p53 on p21WAF1, Bax and cytomegalovirus promoters. The impairment of p21WAF1 transactivation by c-Myc was confirmed by transfection of a c-Myc-estrogen receptor fusion protein and by induction of c-myc by zinc in transfected cells. Also, p53-mediated up-regulation of p21WAF1 mRNA protein were significantly reduced by c-Myc, while Bax levels were unaffected. Consistently, c-Myc increased cyclin-dependent kinase 2 activity in K562 cells expressing p53 in wild-type conformation. These results suggest that c-Myc overexpression may antagonize the pro-apoptotic function of p53, thus providing a molecular mechanism for the frequently observed deregulation of c-myc in human cancer.

Cytogenetics of the chronic myeloid leukemia-derived cell line K562: karyotype clarification by multicolor fluorescence in situ hybridization, comparative genomic hybridization, and locus-specific fluorescence in situ hybridization

The transformation of chronic myeloid leukemia (CML) from a chronic phase to an acute phase is frequently accompanied by additional chromosome changes. Extensive chromosome G-banded studies have revealed the secondary changes are nonrandom and frequently include trisomy 8, isochromosome 17q, trisomy 19, or an extra copy of the Philadelphia chromosome. In addition to these secondary chromosome changes, complex structural rearrangements often occur to form marker structures that remain unidentified by conventional G-banded analysis. The CML-derived cell line, K562, has been widely used in research since it was originally established in 1975. The K562 karyotype however, has remained incomplete, and marker structures have never been fully described. Recent advances in fluorescence in situ hybridization (FISH) technology have introduced the possibility of chromosome classification based on 24-color chromosome painting (M-FISH). In this study, we report a clarified karyotype for K562 obtained by a combination of the following molecular cytogenetic techniques: comparative genomic hybridization (CGH), FISH mapping using locus-specific probes, and M-FISH. Multicolor FISH has identified the marker structures in this cell line. The characteristic marker chromosome in K562 has been confirmed by this study to be a der(18)t(1;18). Multicolor FISH confirmed the identity of marker structures partially identified by G-banding as der(6)t(6;6),der(17)t(9;17),der(21)t(1;21),der(5)t(5;6). In addition M-FISH has revealed a deleted 20q and a complex small metacentric marker comprised of material from chromosomes 1, 6, and 20. A cryptic rearrangement was revealed between chromosomes 12 and 21 that produced a structure that looks like a normal chromosome 12 homologue by G-banding analysis. Finally, M-FISH detected regions from chromosome 13 intercalated into two acrocentric markers.

Large deletions at the t(9;22) breakpoint are common and may identify a poor-prognosis subgroup of patients with chronic myeloid leukemia

The hallmark of chronic myeloid leukemia (CML) is theBCR-ABL fusion gene, which is usually formed as a result of the t(9;22) translocation. Patients with CML show considerable heterogeneity both in their presenting clinical features and in the time taken for evolution to blast crisis. In this study, metaphase fluorescence in situ hybridization showed that a substantial minority of patients with CML had large deletions adjacent to the translocation breakpoint on the derivative 9 chromosome, on the additional partner chromosome in variant translocations, or on both. The deletions spanned up to several megabases, had variable breakpoints, and could be detected by microsatellite polymerase chain reaction in unfractionated bone marrow and purified peripheral blood granulocytes. The deletions were likely to occur early and possibly at the time of the Philadelphia (Ph) chromosome translocation: deletions were detected at diagnosis in 11 patients, were found in all Ph-positive metaphases, and were more prevalent in patients with variant Ph chromosomes. Kaplan-Meier analysis showed a median survival time of 36 months in patients with a deletion; patients without a detectable deletion survived &gt; 90 months. The survival-time difference was significant on log-rank analysis (P = .006). Multivariate analysis demonstrated that the prognostic importance of deletion status was independent of age, sex, percentage of peripheral blood blasts, and platelet count. Our data therefore suggest that an apparently simple, balanced translocation may result not only in the generation of a dominantly acting fusion oncogene but also in the loss of one or more genes that influence disease progression.

Chronic myelogenous leukemia: biology and therapy

Chronic myelogenous leukemia is a myeloproliferative disorder. It is characterized by a biphasic or triphasic clinical course in which a benign chronic phase is followed by transformation into an accelerated and blastic phase. On a cytogenetic and molecular level, most patients with chronic myelogenous leukemia demonstrate BCR-ABL fusion genes in hematopoietic progenitor cells, which result from a reciprocal translocation between chromosomes 9 and 22; this translocation leads to a shortened chromosome 22, called the Philadelphia chromosome. Translation of the fusion products yields chimeric proteins of variable size that have increased tyrosine kinase activity. Conventional chemotherapy with hydroxyurea or busulfan can achieve hematologic control but cannot modify the natural disease course, which inevitably terminates in a rapidly fatal blastic phase. Since its introduction in the 1980s, allogeneic stem-cell transplantation has provided the groundwork for a cure of chronic myelogenous leukemia. However, few patients are eligible for this treatment because of donor availability and age restrictions. Therapy with interferon-alpha alone or in combination with cytarabine suppresses the leukemic clone, produces cytogenetic remissions, and prolongs survival. It is an effective alternative first-line treatment for patients ineligible for transplantation. New drugs active against chronic myelogenous leukemia may show increased activity in the transformed phases of the disease. Novel therapies and concepts are developing rapidly; targeted molecules are tyrosine kinases, ras, and messenger RNA through antisense oligonucleotides. Alternative transplantation options, such as stem cells from autologous sources and matched unrelated donors, are expanding. Immunomodulation by adoptive immunotherapy and vaccine strategies hold significant promise for the cure of chronic myelogenous leukemia.

p53 mediates apoptotic crisis in primary Abelson virus-transformed pre-B cells

Transformation of pre-B cells by Abelson murine leukemia virus (Ab-MLV) involves a balance between positive, growth-stimulatory signals from the v-Abl oncoprotein and negative regulatory cues from cellular genes. This phenomenon is reflected by the clonal selection that occurs during Ab-MLV-mediated transformation in vivo and in vitro. About 50% of all Ab-MLV-transformed pre-B cells express mutant forms of p53 as they emerge from this process, suggesting that this protein may play an important role in the transformation process. Consistent with this idea, expression of p19(Arf), a protein whose function depends on the presence of a functional p53, is required for the apoptotic crisis that characterizes primary Ab-MLV transformants. To test the role of p53 in pre-B-cell transformation directly, we examined the response of Trp53(-/-) mice to Ab-MLV. The absence of p53 shortens the latency of Abelson disease induction but does not affect the frequency of cells susceptible to Ab-MLV-induced transformation. However, primary transformants derived from the null animals bypass the apoptotic crisis that characterizes the transition from primary transformant to fully malignant cell line. These effects do not require p21(Cip-1), a major downstream target of p53; however, consistent with a role of p19(Arf), transformants expressing mutant p53 and abundant p19 retain wild-type p19 sequences.

Comparative analysis of G-banding, chromosome painting, locus-specific fluorescence in situ hybridization, and comparative genomic hybridization in chronic myeloid leukemia blast crisis

The molecular basis for blast transformation of chronic myeloid leukemia (CML) remains poorly understood. Cytogenetic alterations associated with CML blast crisis have previously been extensively studied by conventional G-banding analysis. However the complexity of some chromosome abnormalities or poor chromosome morphology or both has exceeded the resolution of G-banding analysis in a significant proportion of CML cases, and complex chromosome rearrangements have remained unidentified. In this study, comparative genomic hybridization (CGH) was used to elucidate genome imbalances in chronic phase or blast crisis samples or both from 12 CML patients. CGH and G-banding results were compared, and discrepancies were further clarified by using multipaint chromosome analysis and locus-specific DNA probes. No imbalances were detected in the 4 early disease phase samples studied. Eleven blast crisis samples were analyzed by G-banding and CGH, and the commonest genomic abnormality detected was overrepresentation of the long arm of chromosome 8, which was detected in 5 patients. This overrepresentation was attributable to trisomy 8 in 4 patients, whereas amplification of the entire long arm of chromosome 8 was detected in 1 patient. The formation of isochromosomes of the long arm of chromosome 8 was observed as a mechanism for gene amplification in this patient. Additional material originating from chromosome 8 was also observed intercalated into three marker chromosomes in peripheral blood metaphase spreads from this patient. These markers may further define areas on chromosome 8 that harbor oncogenes implicated in transformation of chronic myeloid leukemia.

Correlation between apoptosis and TP53 status in osteosarcoma

Samples of 18 osteosarcomas were examined for the occurrence of apoptosis and TP53 status. Apoptosis was investigated by an in situ nick translation technique on paraffin-embedded samples. It was found that apoptosis rarely occurs in osteosarcoma at the early stage of disease, whereas it is frequently activated when tumors are treated with antiblastic drugs. The analysis of the TP53 gene showed no mutation at diagnosis; whereas, during disease progression, four cases showed TP53 mutations. The authors discuss the relation between apoptosis, TP53 status, and therapy.

The effect of heptachlor, a chlorinated hydrocarbon insecticide, on p53 tumor suppressor in human lymphocytes

Previous studies have shown that heptachlor, a chlorinated hydrocarbon insecticide, is a liver tumor promoter in rats and mice and induces tumor promoting-like alterations in human myeloblastic leukemia cells. The nature of tumor promotion is multifaceted and has recently been shown to include suppression of programmed cell death (apoptosis) as a mechanism by which a tumor promoter can prolong cell viability. The ability of tumor promoters to suppress apoptosis prompted us to address the question of whether heptachlor is capable of effecting the expression of genes involved in lymphocyte apoptosis, in particular, the p53 tumor suppressor gene. Experiments with a CEM x 174 cell line, a hybrid of human T and B cells, revealed that heptachlor downregulated p53 gene expression at the post-transcriptional level without changing levels of mRNA in the cells. The heptachlor-induced reduction in the basal levels of expression of this gene was both in a concentration and time-dependent manner.